432 THE RIGHTING RExiCTIOX IN ASTERINA GIHBOSA. 



of tlie body with I'espect to gravity — the drag or pnll of the 

 internal organs. The existence of this factor was recognized by 

 Preyer {ibid. p. 121), and its importance in Crustacea has recently 

 been emphasized l>y W. von Buddenbrock (1914). As the star- 

 ii.sh shifts its position with respect to gravity the internal organs, 

 or at least such of them as are .slung by mesenteries, must shift 

 their position within the bod}'. It is conceivable that such 

 alterations in stress are perceived by means of an interoceptive 

 nervous mechanism. In Experiment V., for instance, the stimulus 

 to turn to the horizontal may have been supplied by the down- 

 ward drag of the internal organs. 



In conclusion, a remai'k upon method ma)^ perhaps be per- 

 mitted. If the whole reaction is considered as behaviour in the 

 real sense, that is to say, considered strictly from the psychological 

 point of view — as has in effect been done in the above discussion — 

 the problem ought not be formulated in terms of physiological 

 reaction to single environmental stimuli, but in terms of response 

 to a situation presented to the animal as a whole, or, in the case 

 of an experimental dissociation of the normal combined action of 

 the factors involved (as in Experiment lY.), in terms of re.sponse 

 to one factor as representative or suggestive of the whole normal 

 presented situation. 



References to Literature. 



Buddenbrock, W. von. 1914. " Ueber die Orientirung der 



Krebse im Raum." Zool. Jahrb. (Allg.) xxxiv. pp. 479- 



514. 

 Glaser, O. C. 1907. "Movement and Problem Solving in 



Ophiura hrevispina." Journ. Exper. Zool. iv. pp. 203-20. 

 Jennings, H. S. 1907-8. "Behaviour of the Starfish ^4 sierias 



forreri de Loriol." Univ, California Public. Zool. iv. 



pp. 53-185. 

 Plessner, H. 1913. " Unters. U. d. Physiologie d. Seesterne." 



Zool. Jahrb. (A1lg.) xxxiii. pp. 361-86. 

 Preyer, W. 1886-7. "Ueber die Bewegung der Seesterne." 



Mitteil. Zool. Stat. Neapel, vii. ppr27-127 and 191-233. 



